Thermostat device



June 2, 1953y J. B.,cATA| Do ET AL 2,640,896

THERMOSTAT DEVICE Filed March 16, 1950 mm Y Y Y I8 INVENTORS. JOHN B.CATALDO ALBERT N. COOK @WM n #/wq 6 THEIR ATTORNEYS.

Patented June 2, 1953 THERMOSTAT DEVICE J'ohrr E: Cataldo-,Bernardsv/llef, and Albert Cook, Stirlings Ne J .f,. assignors to `lohn4BL Pierce.

Found, New Yori:

ation, New York, N..Y. a corporation of Application March 16, 1950ySerial Non 1495948 Y 3 Glai'ms. l.

This invention relates to' thermorespo'nsive device's'- and moreparticularly to thermostats hav*- inp a nigh degree or sensitivity and ausefuii work outputy capable. of direct control of heavy' loads such,for example', as electricas switch apparatus in power circuits.4

the desi-:gni ofiA tl'i'er'mostats it: is, in. general, necessary toleffect cer-tain. compromises between the operating. aridstructuralcharacteristics tl'iereoi.v ideally a thermostat affords a'A highdeer-ee or sensitivity' coupled withu use'- nily work' output, the'.overall' size andIv mechanical complexity nevertheless being main-tainedwithin practical limits` to facilitate' economical manniacture andiconveniencey or installatiorli. To this end. it has been found that theAdesign of thermostats', particularly those which control electricaloi'rfhiitsy may' be simplified and' otherwise imby the rise ofmoi-iometal'lic snap spring bers, which are adapted to snapy forcefullyand rapidly between two con'gi'irations of equitlibrium once initiatedby a preestablis'hed, externallly` applied thrust, which thrust isgenerally provided by the heat sensing element.

It is, accordinglyy one object of this invention to provide a thermostatwhich is particularly adapted for use in combination with simplifiedheat sensing elements having a small Work output as compared tothe workoutput'ofthe thermo` stat.

lt is another object of theA invention to provide a thermostat combiningrobust structural characteristics with a high degree of' sensitivity,which thermostat may be adapted for a wide variety oi? specialized uses.

It is another' object of the invention to provide a thermostatparticularly adapted for? use as an immersion unit to control watertemperatures, the design being such that the uni-timay be readilymounted in water tanks using standard pipe connections;

The above and other features of the invention may be more readilyunderstood. by reference to the accompanying. drawings or a thermostatformed accordingv to the invention. in which Figi. 1 isvv an: end viewofy ak thermostat ofV the immersion type showing the junctionl boxvassembly;

Fig. 2 is a view in longitudinal cross-section of' the thermostat formedby the plane containing the line 2--2 of Fig. 1, and

Fig. 3v is a view in longitudinal cross-section of the thermostat asformed by the place containing the line 3-3 of Figi. 1..

Referring' to Figs'. 2 and 3 of the drawing, there (Cl. 20G-137) isshownL a thermostat of the immersion type includ-ing... broadly, animmersion tube lo'. affixed at its inner end.: to ai pipe fitting oradaptor H, which inV turni carries a junction box l2 containing certainelectrical switchA mechanism.. In.- terposed between thel junction boxand: the mmersion tube" is a motion-modifying driving linkage indicatedgenerally at lf3 (Figsy 3) whereby comparatively small movements of theheatsensi'ng., means are amplified to provideY forceful and enlargedmovement suitable for operating the. contacts oiv an electrical powercircuit.`

The illustrated unitis designed for use in water-heaters and` the like,and to this end may bel mounted-y by mea-ns of standard pipe connectionsin av convenient: opening M. in` the wally W of` a tank by means ofy a.short length of pipe l5, which may be rolled, threaded; or otherwisesecured in the opening in the wall in the watertight joint. The outer'enct of the' pipe |5- is intern-ally threaded to receive a threadedshank i6f .termed on the pipe fitting il', with the immersion tube Hl5projecting through the. pipeand into.y the tank. for aconvenientdis-tance to be enveloped by the water or other fluidv medium therein.

The immersion tube to comprises an outer sleevey Il., formed of amaterial,` such` for exampleas Invar, having a low coemcienti of thermalexpansion- Wi'thin the range of operation of the thermostat, The sleevell1 is supported. at its inner end in' a water-tight joint in a recessyt8 formed in the shan-kY of thev pipe fitting. Il.y An elongated.y rodyI9',I formed oi? a material having a high coeincient of expansionrelative to the sleeve H, such as brass; for example,l is receivedwithin the sleeve Il: iny a.y snug; but sliding nt, the outerA of' therod being formed with athreaded tip 2ty which screws into a. tapped plug2! rigidly securedA in the tree' end' oi sleeve I1. The: tip 20 may belformed' with a screw-driver' slot 20a to facilitate limited lengthwiseadjustment ofv the rass' rod within the' sleeve.

The inner end of the brass rod. passes` through a central bore 22.formed inA the shank` of the pipe ntting H and enters an enlarged cavity23 also formed: in the pipe fitting. A pair of cooperating lever' arrns24v and 25 are pivotally mounted` within the cavity, with the edge ofthe lever 24 being engaged. by the' nose end of the brass rod 1.8 tolprovide a motion-modifying.' linkage which amplies expansion movement ofthe brass rod by a factor of lathe output of the linkage being taken oitat the" tip of the lever 25.L

junction box l2, comprising: a cup-shaped shell portion 26 formed withan opening 26a adjacent the mouth of the cavity I3, is secured to thepipe fitting H by means of three flat-headed screws 21, with a gasket 28interposed therebetween. A plate member 29, formed with a cavity 29a anda central bore 29D, is bolted together with a domed cap member 30 to theshell 26 by means of four through-bolts 3l, with gaskets 32 and 33 beinginterposed between contiguous surfaces of the shell and plate and plateand cap respectively.

Mounted within the cavity 29a is a monometallic snap disc springperipherally loosely confined between an annular shoulder 34 and awasher 35. The snap disc 35 is thus mounted so that its central portionmay partake of snap movement between either of two configurations ofequilibrium as shown in full and broken lines in Figs. 2 or 3. Snapdiscs of the type contemplated herein may be formed according todisclosures in the following pending U. S. patent applications: SerialNo. 628,447, liled November 14, 1945, entitled Toggle Springs, nowPatent No. 2,571,170, patented October 16, 1951; Serial No.

635,956, led December 19, 1945, entitled Snap Disc Springs, now PatentNo. 2,604,316, patented July 22, 1952; and Serial No. 139,182, filedJanuary 18, 1950, entitled Snap Disc Springs and Methods of Manufacture.According to those disclosures a snap disc may be made so that its snapmovement in one direction may be initiated with comparative ease,whereas the return movement may reduire considerably greater force.

In the instant invention, the disc is preferably made so that it may besnapped out of its configuration as shown in full lines in Figs. 2 or 3with an initiating thrust such as may be aorded by the output lever 25of the amplifying linkage I3. Thus the snap spring disc in theillustrated embodiment is formed so that the successive trippointsthereof measured from any reference, such as the normal plane of thedisc, do not vary more than $0.001 inch or a total of 0.002 inch. Asensitivity or variation of only 2 is possible at the calibratedtemperature level of the device. Accordingly, with the brass rod l1partaking of an expansion movement of 0.0001 inch per degree Fahrenheit(the brass rod being approximately nine inches in length), and with amultiplying factor of ten provided by the levers 24 and 25, the centerof the disc 35 will be displaced .001 inch per degree F. A change of 2degrees in temperature of the water above the preestablished maximumwill, therefore, initiate snapping of the disc.

The sensitivity of the unit may be adjusted within preestablished limitsby adjusting the brass rod i9 lengthwise within the Invar sleeve l1,this being accomplished by turning the threaded tip 20 either toincrease or decrease the pressure normally exerted against the disc 35.

The mechanism to be actuated by the snap movement of the disc 35 may beof any suitable type, with the preferred embodiment comprising anelectrical switch assembly hereinafter described. The central bore 29hof the plate member 29 slidably receives a push-rod 31 formed with aretaining shoulder 38. 'Ihe inner end of the rod 31 is adapted to beengaged by the moving portion of the disc 35 upon snapping into thesecond configuration of equilibrium as shown in broken lines.

Mounted within the dome of the cap member 30 is a movable carrier plate39 formed of insulating material and centrally apertured toreceive apush-button extension 31a formed on the end of the push-rod 31. Theinner surface of the carrier plate 39 is engaged by the shoulder 38 ofthe push-rod 31 so that movement of the pushrod effects a correspondingmovement of the plate. A pair of shorting arms 4l), formed ofelectrically conducting material, are loosely secured at their centersto the under-side of the carrier plate 39 by means of rivets 4l.

Each of the two shorting arms 40 carries a pair of contact elements 42and 43, and two pairs of stationary contacts 44 and 45 are mounted inthe plate 29 to be engaged by movable contacts 42 and 43 respectively.Conductor strips 46 and 41 (Fig. l), are connected to the stationarycontacts 44 and 45 respectively, and are furnished with suitableterminal screws 49 and 49 at their outer ends.

The carrier plate 39 is formed on its upper surface with a pair ofbosses 50 and 5| over which are fitted compression springs 52 and 53which react against the inner surface of the cap 30 to urge the carrierdownwardly to close all contacts.

In operation, as the temperature of the surrounding medium in the tankis raised to the preestablished value, the brass rod I9 will expand and,through the levers 24 and 25, will snap the disc 35 to its secondconiiguration of equilibrium. In so doing the push-rod 31 will be drivenupwardly against the force of thc coil springs 52 and 53 to open thenormally-closed pairs of contacts 42-44 and 43-45. The characteristicsof the disc 35 are such that it is able to maintain its secondconfiguration of equilibrium against the action forces of the compressedsprings 5| and 52.

In order to effect resetting of the thermostat after the watertemperature within the tank has been lowered, the push-button extension31a may be pressed by means of key or other suitable instrument througha convenient opening 54 in the cap member 30, thereby to drive the innerend of push-rod 31 against the snap disc 35 to initiate snappingmovement in the reverse direction.

Numerous modifications may be provided in the above described thermostatwithout departing from the scope of the invention. Thus for example,various heat responsive devices may be utilized in place of the brassrod i8 and Inval' sleeve l1, it being required only to revise theampliiication factor of the motion-modifying linkage according to thecharacteristic of the heat responsive member used. If preferred the heatresponsive element may be made to induce the resetting action of thedevice by providing a suitable driving connection therebetween. Likewisenumerous modications may be made in the design and characteristics ofthe electrical circuit actuated by snap movement of the disc 35.Accordingly, it Will be apparent that the invention should not belimited in scope save as defined by the following claims,

We claim:

1. In a thermoresponsive device having thermal sensing means adapted toprovide a limited output movement in response to a preestablishedtemperature diiferential, a housing having a first chamber formedtherein, an axially movable shaft member extending into said chamber andhaving a shoulder formed thereon, movable plate means in the chamberhaving a central aperture to receive said shaft and engaging saidshoulder, iirst and second spring means disposed on opposite` sides ofthe axis of said shaft member reacting between said housing and saidplate means, first and second pairs of stationary contacts mounted insaid chamber, contact means on said plate means, said contact meansbeing adapted to complete electrical circuits between each of said pairsof stationary contacts, a snap spring disc adapted to partake of snapmovement between tWo coniigurations, annular abutment means for looselyconning said disc adjacent its periphery, said sensing means beingadapted'to engage the center portion of said disc to induce snapmovement between said configurations, 4the inner end of said movableshaft member being spaced from the center of said disc in one of saidconiigurations but disposed within the range of travel of the disc tothe other configuration, thereby to be engaged and displaced by saiddisc after snap movement is initiated by said sensing means, thedisplacement of said movable shaft member being adapted to displace saidplate means and contact means thereon to open the circuits between saidstationary contacts.

2. A thermoresponsive device as set forth in claim 1, said movable platemeans comprising a plate member of electrically insulated material, anda pair of arched electrically conducting arms carried by theirrespective centers by said iplate member, said contact means beingdisposed at the free ends of said arms, whereby the electrical circuitbetween the respective pairs of stationary contacts is adapted to becompleted through said arms.

3. A thermoresponsive device as set forth in claim 1, including achannel formed in said housing adjacent said movable shaft memberaffording access to the shaft member by means of which the shaft membermay be manually actuated to cause the snap spring disc to reverse itsconfiguration and to permit said first and second spring means to closethe electrical circuits between the said .pairs of stationary contacts.

JOHN B. CATALDO. ALBERT N. COOK.

References Cited in the le 0f this patent UNITED STATES PATENTS

